Polishing compositions containing charged abrasive

ABSTRACT

Polishing compositions that can selectively and preferentially polish certain dielectric films over other dielectric films are provided herein. These polishing compositions include either cationic or anionic abrasives based on the target dielectric film to be removed and preserved. The polishing compositions utilize a novel electrostatic charge based design, where based on the charge of the abrasives and their electrostatic interaction (forces of attraction or repulsion) with the charge on the dielectric film, various material removal rates and polishing selectivities can be achieved.

FIELD OF THE DISCLOSURE

This invention relates to polishing compositions, and methods forpolishing semiconductor substrates using the same. More particularly,this invention relates to chemical mechanical polishing compositions andmethods for selectively removing certain dielectric layers from asemiconductor substrate.

BACKGROUND OF THE DISCLOSURE

The semiconductor industry is continually driven to improve chipperformance by further miniaturization of devices by process andintegration innovations. Chemical Mechanical Polishing/Planarization(CMP) is a powerful technology as it makes many complex integrationschemes at the transistor level possible, thereby increasing chipdensity. Not surprisingly, there are a multitude of new CMP steps andrequirements at the Front End of Line (FEOL) transistor fabricationstep. The FEOL material stack typically includes a metal gate andmultiple stacks of dielectric materials. The prevalently used dielectricfilms are Silicon Nitride (SiN), Silicon Oxide (SiO₂ or TEOS),Poly-silicon (P—Si), Silicon Carbon Nitride (SiCN), Spin On Carbon (SOC)carbon hard mask, and low-k/ultra-low k (SiCOH, SiOC) dielectric films.With the introduction of high-k metal gate technology at 45 nm andFinFET technology at 22 nm chip production by Intel Corporation, SiN,SiO₂, SiCN and P—Si films started being used more profusely, and in agreater number of applications in FEOL. Additionally, in Back End ofLine (BEOL) applications, with resistivity of conventional barriermaterials (Ta/TaN; Ti/TiN) not scaling down for advanced sub-10 nmmanufacturing nodes, semiconductor companies are using dielectrics suchas SiN, SiO₂, and P—Si for various BEOL material stacks. For both FEOLand BEOL, these dielectric films can be used as an etch stop layer,capping material, spacer material, additional liner,diffusion/passivation barrier, hard mask and/or stop-on layer.

SUMMARY OF THE DISCLOSURE

Thus, dielectric films are being used much more profusely in advancedsemiconductor manufacturing. From a CMP perspective, most of theseintegrations incorporating dielectrics require polishing compositions(slurries) that can work/polish (or stop) on either two or three ofthese films. For example, it is desirable to develop a slurry that canremove SiN and not remove (stop on) SiO₂/P—Si or a slurry that canremove SiO₂ and not remove (stop on) SiN. For designing such systemswith multiple requisites, the traditional approach has been to add somechemical enhancers or inhibitors that can enhance or inhibit the ratesof one or more of these dielectric films. A classic example is ShallowTrench Isolation (STI) slurries that use amino acids as chemicals thatfurther inhibit the rates of SiN in formulations containing ceriaabrasive. These STI slurries polish TEOS selective to SiN, and displayhigh TEOS rates and stop (or have near to zero polish rates) on SiNfilms.

It is noteworthy that dielectric (SiN, TEOS, P—Si) films, albeit solidsurfaces, have electrostatic charges. The charge (positive, negative orzero) manifests itself as zeta potential, and varies with pH. Similarly,abrasives (for example silica) as colloidal dispersions have their owncharges and zeta potential values that vary with pH. Furthermore, theseabrasives can be surface modified to exhibit negative zeta potential(e.g., anionic silica) or positive zeta potential (e.g., cationicsilica). Thus, both the abrasives and dielectric films haveelectrostatic charges, and if an abrasive and a dielectric film havedissimilar charges (positive vs. negative) at a particular pH, therewill be attraction between the two that will consequently lead to highremoval rates of that particular film using that particular abrasive.Conversely, if an abrasive and a dielectric film have similar charges(either both positive or both negative), there will be repulsion forcesbetween the two, leading to low (e.g., close to zero) removal rates andstopping on that dielectric film using that particular abrasive. Thus,the electrostatic attraction and repulsion are driven by the surfacecharge (among other things) and thus by the liquid slurry/abrasive zetapotential and the zeta potential of the solid dielectric surface. Thisdisclosure teaches a design of polishing compositions (slurries)containing charged abrasives for selectively and preferentiallypolishing substrates containing multiple dielectric films such assilicon nitride, silicon oxide, poly-silicon, silicon carbon nitride,and low/ultra-low k dielectric films. This CMP slurry design isprimarily based on taking advantage of electrostatic forces ofattraction and/or repulsion between the abrasive and the dielectricfilms.

In general, the present disclosure relates to aqueous polishingcompositions that can selectively and preferentially polish somedielectric films over others in substrate containing multiple dielectricfilms. More particularly, the present disclosure discusses designing ofpolishing compositions (slurries) for selective material removal basedon the surface charge of the abrasives and the surface charge of thedielectric films. If the surface charge of the abrasive has the samepolarity as that of the dielectric film, the two materials repel,thereby decreasing the removal rates (RRs) of the dielectric film.Conversely, if the surface charge of the abrasive has a polarityopposite to that of the dielectric film, then, there are attractionforces between the two materials and RRs of that dielectric filmincrease. This concept of surface charged based attraction/repulsionforces and RRs depending on these forces is illustrated in FIG. 1. Ascan be seen in FIG. 1, using charged abrasives (e.g., anionic orcationic silica) can help design systems for selectively removing adielectric material versus another dielectric material. For example, inFIG. 1, Case I shows that by using anionic silica (negatively chargedsilica with a negative zeta potential), polishing compositions canselectively polish SiN dielectric (which has a positive zeta potential)at high RRs, and simultaneously polish SiO₂/low-k/P—Si dielectricmaterials (which have a negative zeta potential) at very low removalrates. Conversely, in FIG. 1, Case II shows that by using cationicsilica (positively charged silica with a positive zeta potential),polishing compositions can selectively polish SiO₂/low-k/P—Si dielectricmaterials at high RRs (due to attraction forces), and simultaneouslypolish SiN dielectric at very low RRs. In some embodiments, this chargebased design concept can be applicable for the acidic 2-7 pH range.

The concept of designing slurries for polishing dielectrics based on thecharge of the abrasive is further summarized in the table in FIG. 1. Ascan be seen from the Table in FIG. 1, SiN films can be selectively andpreferentially polished over other dielectrics using anionic abrasives(Case I) whereas SiO₂/low-k/P—Si dielectric films can be selectively andpreferentially polished over SiN films using cationic abrasives (CaseII).

Thus, in one aspect, the present disclosure provides a polishingcomposition. The composition includes an anionic abrasive, an acid/basepH adjuster and water. The polishing composition has a pH of about 2 toabout 7. In this embodiment, by using an anionic abrasive, a polishingcomposition can selectively and preferentially polish SiN overSiO₂/low-k/P—Si films (FIG. 1: Case I). For example, the polishingcomposition can exhibit a first rate of removal of silicon nitride, asecond rate of removal of polysilicon, and a ratio of the first rate tothe second rate is at least about 2:1.

In another aspect, the present disclosure provides a polishing methodthat includes (a) applying a polishing composition to a substrate havingsilicon nitride and polysilicon on its surface, and (b) bringing a padinto contact with the substrate and moving the pad in relation to thesubstrate. The composition includes an anionic abrasive, an acid/base pHadjuster and water. The polishing composition has a pH of about 2 toabout 7. The method can remove at least a portion of silicon nitride ata first rate, the method removes at least a portion of polysilicon at asecond rate, and a ratio of the first rate to the second rate is atleast about 2:1.

In another aspect, the present disclosure provides polishingcompositions and polishing methods that polish SiO₂/low-k/P—Si filmswith high selectivity and high polishing rates over SiN dielectricfilms. The polishing composition can include a cationic abrasive, anacid/base pH adjuster and water. The polishing composition has a pH ofabout 2 to about 7. In this embodiment, using a cationic abrasive, apolishing composition can selectively and preferentially polishSiO₂/low-k/P—Si films over SiN (FIG. 1: Case II). In some embodiments,the cationic abrasive can include alumina, silica, titania, zirconia, aco-formed product thereof, or a mixture thereof. In some embodiments,the cationic abrasive can include ceria having a mean particle size offrom about 1 nm to about 5000 nm. In some embodiments, the polishingcomposition containing a cationic abrasive is substantially free of ahalide salt.

In yet another aspect, this disclosure provides a polishing method thatincludes (a) applying a polishing composition to a substrate havingsilicon nitride and at least one of silicon oxide and polysilicon on asurface of the substrate, wherein the composition includes a cationicabrasive, an acid or base, and water, and the composition has a pH ofabout 2 to about 7; and (b) brining a pad into contact with thesubstrate and moving the pad in relation to the substrate. The methodremoves at least a portion of at least one of silicon oxide andpolysilicon at a first rate, the method removes at least a portion ofsilicon nitride at a second rate, and a ratio of the first rate to thesecond rate is at least about 2:1.

In yet another aspect, the present disclosure provides polishingcompositions containing anionic/cationic abrasives having a long shelflife, with respect to the usable time period and/or expiration date ofthe composition. Particularly, the colloidal dispersion stability asmeasure by the zeta potential of polishing compositions containinganionic/cationic abrasives is compared and contrasted to compositionshaving normal/non-ionic colloidal silica. In general, normal/non-ioniccolloidal silica is unsuitable (by itself) for use in the acidic pHregime for polishing dielectric films. Thus, polishing compositionscontaining anionic/cationic abrasives are far superior to non-ionicsilica for use in polishing a substrate containing multiple dielectricsdue to superior composition stability of charged abrasives in acidic pHregime.

In yet another aspect, the compositions of the present disclosure can bediluted at the point of use (POU) (i.e., before going on the polishingtool) without changing the CMP performance. For example, theconcentrated polishing composition can be 2× of POU. When CMP isperformed by diluting the 2× with water to reach components'concentration of 1× formulated slurry at POU, there is no deteriorationin performance of the concentrate formulation (2×) versus the dilutedformulation (1×). More concentrated polishing compositions (such as 3×,5×, 10×, etc.) can be prepared using similar methodology.

Embodiments can include one or more of the following features:

In some embodiments, the composition containing a cationic abrasive canhave a first rate of removal of silicon oxide or polysilicon, a secondrate of removal of silicon nitride, and a ratio of the first rate to thesecond rate is at least about 2:1 (e.g., at least about 8:1).

In some embodiments, the composition containing an anionic abrasive canhave a first rate of removal of silicon nitride, a second rate ofremoval of polysilicon, and a ratio of the first rate to the second rateis at least about 2:1 (e.g., at least about 8:1).

In some embodiments, the cationic or anionic abrasive can include ceria,alumina, silica, titania, zirconia, a co-formed product thereof, or amixture thereof. In some embodiments, the cationic or anionic abrasivecan include colloidal alumina, colloidal silica, colloidal ceria orcolloidal titania. In some embodiments, the cationic abrasive caninclude cationic colloidal silica, or base immobilized non-ionic silica.In some embodiments, the anionic abrasive can include anionic colloidalsilica, or acid immobilized non-ionic silica. In some embodiments, thesilica can be prepared by a sol-gel reaction from tetramethylorthosilicate. In some embodiments, the cationic abrasive can includeterminal groups of formula (I):—O_(m)—X—(CH₂)_(n)—Y  (I),in which m is an integer from 1 to 3; n is an integer from 1 to 10; X isAl, Si, Ti, or Zr; and Y is a cationic amino or thiol group. In someembodiments, the anionic abrasive can include terminal groups of formula(I):—O_(m)—X—(CH₂)_(n)—Y  (I),in which m is an integer from 1 to 3; n is an integer from 1 to 10; X isCe, Al, Si, Ti, or Zr; and Y is an acid group. In some embodiments, thecationic or anionic abrasive can be present in the composition in anamount of from about 0.01 wt % to about 50 wt % based on the totalweight of the composition.

In some embodiments, the acid can be selected from the group consistingof formic acid, acetic acid, malonic acid, citric acid, propionic acid,malic acid, adipic acid, succinic acid, lactic acid, oxalic acid,hydroxyethylidene diphosphonic acid, 2-phosphono-1,2,4-butanetricarboxylic acid, aminotrimethylene phosphonic acid,hexamethylenediamine tetra(methylenephosphonic acid),bis(hexamethylene)triamine phosphonic acid, amino acetic acid, peraceticacid, potassium acetate, phenoxyacetic acid, glycine, bicine, diglycolicacid, glyceric acid, tricine, alanine, histidine, valine, phenylalanine,proline, glutamine, aspartic acid, glutamic acid, arginine, lysine,tyrosine, benzoic acid, nitric acid, sulfuric acid, sulfurous acid,phosphoric acid, phosphonic acid, hydrochloric acid, periodic acid, andmixtures thereof. In some embodiments, the base can be selected from thegroup consisting of potassium hydroxide, sodium hydroxide, cesiumhydroxide, ammonium hydroxide, triethanolamine, diethanolamine,monoethanolamine, tetrabutylammonium hydroxide, tetramethylammoniumhydroxide, lithium hydroxide, imidazole, triazole, aminotriazole,tetrazole, benzotriazole, tolytriazole, pyrazole, isothiazole, andmixtures thereof. In some embodiments, the acid or base can be presentin the composition in an amount of from about 0.0001 wt % to about 30 wt% based on the total weight of the composition.

In some embodiments, the cationic or anionic abrasive has a meanparticle size of from about 1 nm to about 5000 nm.

In some embodiments, the polishing composition containing a cationicabrasive can have a zeta potential of from about 0 mV to about +100 mV.In some embodiments, the polishing composition containing an anionicabrasive can have a zeta potential of from about 0 mV to about −100 mV.

In some embodiments, the polishing composition can have a conductivityof from about 0.01 mS/cm to about 100 mS/cm.

In some embodiments, the zeta potential difference between the polishingcomposition containing a cationic abrasive and silicon oxide orpolysilicon is greater than 20 mV and the zeta potential differencebetween the polishing composition containing a cationic abrasive andsilicon nitride in less than 20 mV. In some embodiments, the zetapotential difference between the polishing composition containing ananionic abrasive and silicon nitride is at least about 20 mV and thezeta potential difference between the polishing composition containingan anionic abrasive and polysilicon is at most about 20 mV.

In some embodiments, the polishing method using a polishing compositioncontaining a cationic abrasive removes substantially all of the at leastone of silicon oxide and polysilicon on the substrate. In suchembodiments, the polishing method can further include a step of removingat least some (e.g., substantially all) of silicon nitride on thesubstrate.

In some embodiments, the polishing method using a polishing compositioncontaining an anionic abrasive removes substantially all of siliconnitride on the substrate. In such embodiments, the polishing method canfurther include a step of removing at least some (e.g., substantiallyall) of polysilicon on the substrate.

In some embodiments, the substrate can further include an additionalmaterial selected from the group consisting of metals, metal oxides,metal nitrides and dielectric materials. In some embodiments, thepolishing method can further include producing a semiconductor devicefrom the substrate treated by the polishing composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides an overview of the abrasive charge based design conceptfor selectively polishing various dielectrics. Case I (left) details anexample where anionic abrasives are used to polish SiN selectively andstop on TEOS (SiO₂ films)/low-k/P—Si dielectric films. Case II (right)depicts an example wherein cationic abrasives are used to selectivelypolish TEOS (SiO₂ films)/low-k/P—Si dielectric films and stop on SiNfilms. The table at the bottom of FIG. 1 summarizes the type of chargedabrasives (anionic/cationic) suitable for the type of polishingcomposition design and application.

FIG. 2 shows the zeta potential of various dielectric films (SiN,SiO₂(TEOS), & P—Si) and silica types (normal/non-ionic colloidal silica(S), Cationic silica (C), and Anionic silica (A)) in the pH range of2-11. Further, FIG. 2 demonstrates that in the pH range of 2-7, as perthe zeta potential, the C silica repels with SiN films, and attracts toSiO₂(TEOS) and P—Si films, whereas the A silica attracts to SiN filmsand repels with SiO₂(TEOS) and P—Si films.

FIG. 3 shows the charge based design concept using anionic abrasivesbased on the data obtained in Example 1 (Case I shown in FIG. 1). Basedon FIG. 3, it is believed that when anionic abrasives are used in CMPslurry formulations, the negative charge on the abrasives attracts tothe positive charge on SiN films (see zeta potentials) and gives highCMP removal rates (RRs) of SiN films. Conversely, it is believed thatSiO₂ (TEOS) films have negative charge (like anionic abrasives) andrepel the abrasives, thus causing the CMP formulations containinganionic abrasives to stop on, or exhibit very low CMP RRs on, SiO₂(TEOS) films.

FIG. 4 shows another scenario of Case I based on the data obtained inExample 2. Based on FIG. 4, it is believed that using anionic abrasivesresults in high CMP removal rates (RRs) on SiN films due to attractionforces between dissimilar charges. Conversely, it is believed that,since anionic abrasives and P—Si films have similar negative charge,they repel each other and, thus, polishing compositions containinganionic abrasives give very low CMP RRs on P—Si films (or stop on P—Sifilms).

FIG. 5 shows one scenario of the charge based design concept usingcationic abrasives based on the data obtained in Example 3 (Case IIshown in FIG. 1). It is believed, when cationic abrasives are used inCMP slurry formulations in acidic pH regime, the positive charge on theabrasives attracts to the negative charge on SiO₂ (TEOS) films (see zetapotentials) and gives high CMP removal rates (RRs) of SiO₂ (TEOS) films.Conversely, it is believed that SiN films have positive charge (likecationic abrasives) and repel the cationic abrasives, thus causing theCMP formulations containing cationic abrasives to stop on, or exhibitvery low CMP RRs on, SiN films.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure provides polishing compositions as well asmethods of polishing substrates using the same. The polishingcompositions generally comprise (a) a cationic or anionic abrasive, (b)an acid and/or base as a pH adjustor, and (c) water. The polishingcompositions can have a pH of about 2 to about 7. The polishingcompositions of the present disclosure can selectively andpreferentially polish or remove dielectric (Silicon Nitride (SiN),Silicon Oxide (TEOS: tetra-ethyl ortho-silicate), Poly-silicon (P—Si),and low-k/ultra-low k (SiCOH) dielectric) films due to uniqueelectrostatic charge interactions of the “charged” abrasive, and thecharge on the surface of the solid dielectric films. This uniqueabrasive and dielectric film charge interaction based polishingcomposition (slurry) design to provide advantageous CMP material removalrates (RRs) is the subject of this invention disclosure. Such polishingcompositions can also be used to polish materials/film stacks thatinclude metals such as cobalt, copper, tungsten, tantalum, titanium,ruthenium, aluminum and their nitrides and oxides, in addition to thedielectric films described above.

The polishing compositions in the present disclosure generally includecharged abrasives: either an anionic (negatively charged) abrasive or acationic (positively charged) abrasive. In general, a polishingcomposition (e.g., a colloidal dispersion) containing a charged abrasivehas an electrostatic charge as seen in zeta potential plots. The zetapotential, also sometimes known as the electrokinetic potential,describes the charging behavior at a solid-liquid interface. In otherwords, the interfacial charge distribution at a solid-liquid interfaceis called the zeta potential.

Anionic abrasives are colloidal abrasives that have been imparted with anegative charge and show negative potential values (in mV) in zetapotential plots, whereas cationic abrasives show positive zeta potentialvalues (see FIG. 2; pH 2-6). Typically, non-ionic/conventional colloidalsilica dispersions (colloidal silica (S) in FIG. 2) are somewhatunstable in the acidic pH regime due to their small zeta potentials.

In general, zeta potential is a good indicator of dispersion stabilityfor abrasive dispersions as well as CMP polishing composition (slurry)dispersions containing those abrasives. In addition, thin films such asSiO₂ films, SiN films, and P—Si films also have zeta potentials (seeFIG. 2). The zeta potential measures the potential difference betweenthe dispersion medium and the stationary layer of fluid attached to thedispersed particle (sometimes also referred to as the potentialdifference in the interfacial double layer at the location of theslipping plane versus a point in the bulk fluid away from theinterface). Zeta potential is expressed in mV, and measures theelectrophoretic mobility of the particles. The zeta potential ofdispersions (abrasive containing colloidal dispersions or polishingdispersions containing abrasives) can be measured by commerciallyavailable tools such as the AcoustoSizer II tool made by ColloidalDynamics, or Malvern tool made by Malvern Instruments. Whereas theAcoustoSizer is based on acoustics technology, the Malvern tool is basedon dynamic light scattering principles. Similarly, the zeta potential(ZP) of solid surfaces such as dielectric films or polishing pads can bemeasured using a SurPASS tool from Anton Paar. For example, the ZP ofSiN, SiO₂ (TEOS) and P—Si dielectric films shown in FIG. 2 were measuredusing the SurPASS 3 tool from the vendor Anton Paar.

The zeta potential is particularly useful in determining colloidaldispersion stability as it is indicative of the electrostatic repulsiveforces between particles. The greater the absolute value of the zetapotential for an electrostatically stabilized dispersion system, thegreater the repulsion forces and the greater the stability of thecolloidal dispersion. If the repulsion forces are small (smaller zetapotential values), particles tend to attract to each other and thusagglomerate/coagulate/lump, leading to dispersion instability. A generalguideline, as per colloid chemistry principles would be as follows:

Stability (with time) of Colloidal Zeta Potential (mV) Dispersion from 0to ±10 Immediate coagulation, gelling and settling from ±10 to ±20 Lessstable from ±20 to ±30 Moderately stable from ±30 to ±60 Good stabilityMore than ±60 Excellent stability

Zeta potential is related to particle surface charge and the pH of thedispersion medium. Abrasives particles such as ceria, alumina, silica,titania, and zirconia have surface charge in their colloidal dispersionstate. This surface charge changes with pH, and the indirectmanifestation of this change in surface charge is the zeta potentialvalue. As the zeta potential (ZP) changes with pH, there might be aparticular pH value at which the ZP of the system is zero. Thiscondition of zero zeta potential (at a particular pH) is referred to asthe isoelectric point (IEP). A dispersion system at IEP is generallyvery unstable and the particles at the IEP pH may agglomerate, therebyincreasing the particle size. Non-ionic colloidal silica is unstable inthe acidic pH regime as it has 2 IEPs (at pH ^(˜)2 and pH ^(˜)4) inacidic conditions (see FIG. 2; Colloidal Silica (S)). Thus, it istechnically very difficult to use non-ionic colloidal silica inpolishing compositions (slurries) which have operating pH in the 2-5range, since the abrasive in unstable (as ZP is 0 to ±10; see FIG. 2)and causes agglomeration/gelling and an increase in particle size ofthese CMP slurries. This increase in particle size of the CMP slurriesis detrimental as it leads to scratches and defects on the wafers duringpolishing and causes inconsistent CMP material removal rates (RRs)across the wafer and dies, thus ultimately resulting in device failure.Therefore, it is desirable to have abrasives (such as silica) that arestable in the acidic pH regime so that CMP slurries containing thosestable abrasives could be formulated. Furthermore, most FEOL slurriesthat are used to polish dielectrics operate in the acidic pH range,re-emphasizing the need to have colloidal stable abrasive dispersions inacidic pH. Thus, to increase the stability of abrasive particles, thesurface of the abrasives can be modified with anionic or cationic groupsto impart negative/positive charge on these abrasives, therebyincreasing their absolute zeta potential values and making the sameparticles stable in the acidic pH regime. For example, some of theterminal silanol (Si—O—H) groups of non-ionic silica (FIG. 2; ColloidalSilica (S)) can be modified by terminal cationic groups to obtaincationic silica (C Silica) that has >+30 mV ZP in the 2-5 pH range, andis thus a stable colloidal dispersion (FIG. 2; Cationic silica (C)) inthis pH range. Similar modification of non-ionic silica with anionicgroups can lead to anionic silica (A silica) that has about −50 mV ZP inthe entire 2-8 pH range (FIG. 2; Anionic silica (A)).

In this invention disclosure, the zeta potentials (ZPs) of the modifiedcationic/anionic silica and the ZPs of three prevalent dielectric films:SiN, SiO₂(TEOS) and P—Si have been carefully analyzed. The ZPs of all 6of these materials (3 silica types and 3 film types) are shown in FIG.2. Without wishing to be bound by theory, the present inventionpostulates that in the acidic pH range of 2-7, based on the ZPvariations of these 6 materials, and the electrostaticrepulsion/attraction forces between a charged abrasive and a film type,various selective FEOL dielectric CMP slurries can be formulated. Inaddition, CMP polishing data on dielectrics presented in Examples 1-3below corroborate the hypothesis that polishing compositions canpreferentially and selectively polish dielectric films based on thecharges of abrasive particles and the charges of the films to beremoved, on a semiconductor substrate. This disclosure exploits zetapotential variations (value, polarity) of abrasives and dielectric films(see FIG. 2), and takes advantage of electrostatic charge interactionsto deliver desirable CMP polishing performance.

Charged abrasives, in the context of this disclosure, refer to abrasivesthat have been surface modified and thus possess either a positivecharge (cationic abrasives) or a negative charge (anionic abrasives).For example, non-ionic colloidal silica can have some of its terminalsilanol (Si—O—H) groups modified by a silane coupling agent. A silanecoupling agent is typically of the formula:(RO—)₃Si—(CH₂)_(n)-anionic/cationic group;  1where R is alkyl (such as methyl (CH₃) or ethyl (CH₃CH₂)); n is thenumber of CH₂ groups in the coupling agent (typically n has a valuebetween 1 and 10); and anionic/cationic group refers to the end terminalgroup for the type of charged silica (anionic vs. cationic). This silanecoupling agent can be reacted with non-ionic silica by a hydrolysis andcondensation reaction to give charged/modified silica. This reaction isshown below:Si—O—H/SiO₂+(RO—)₃Si—(CH₂)_(n)-anionic/cationic group→Charged Silica  2

The charged silica in reaction 2 contains silica (SiO₂), some remainingsilanol groups (Si—OH), and some siloxane (—Si—O—Si—O—) bonding thesilane coupling agent's cationic/anionic groups((—O—)₃Si—(CH₂)_(n)-anionic/cationic) to the silica. Once non-ionicsilica is modified by these silane coupling agents, the zeta potentialof the modified silica changes, and these “charged” dispersions nowbecome stable in the acidic pH regime.

In some cases, to form anionic silica, a suitable silane coupling agentcan be mercaptoalkyltrimethoxysilane (e.g.,3-mercaptopropyltrimethoxysilane). In such embodiments, after the silanecoupling reaction shown above (see Reaction 2) is completed, theterminal —SH (thiol) group can be oxidized using hydrogen peroxide (oranother oxidizer) to form terminal —SO₃H groups on the modified anionicsilica.

The zeta potentials of silica before (non-ionic silica (S)) and of aftermodification (cationic (C) & anionic (A) silica) are shown in FIG. 2.Negative zeta potential indicates that the particle surface isnegatively charged (anionic) in the dispersion, and vice versa forcationic abrasive (positively charged). Non-ionic abrasives are modifiedinto charged abrasives by attaching anionic/cationic groups to some ofthe abrasive particles. This modification to produce a charged abrasiveby chemical bonding with a silane coupling agent is shown above.However, other methods such as physically forming self-assembledmultiple monolayers on top of the silica particles, or physicaladsorption of the anionic/cationic groups on the surface of silicaparticles can be employed to obtain charged abrasives. Furthermore, the“anionic silica” modified from “non-ionic silica” can also be done byintroducing cationic species such as ammonium, sodium, potassium, oraluminum cations. This is especially true in the case of Water-Glasssilica (inorganic silica made from sodium silicate (water glass) rawmaterial) wherein the incorporation of aluminum (Al) into the surface ofthe particle leads to the formation of —Al—OH groups. This results invery highly negatively charged surfaces (anionic silica) in the 2-6 pHregimes. Conversely, for cationic sols from water-glass silica, thesurface can be coated with Aluminum Oxide (Al₂O₃). This makes the chargeon the surface of the silica positive (cationic silica), especially atacidic pH values below pH of 4.

The silica (cationic or anionic) used in the polishing compositions ofthis disclosure can be prepared from any one of the four most prevalentsilica preparation methods used in the CMP industry: 1) organic silicaobtained by a sol-gel reaction (including hydrolysis and condensation)of TetraMethyl OrthoSilicate (TMOS: Si(OCH₃)₄) as a precursor/startingmaterial, 2) organic silica obtained by a sol-gel reaction (includinghydrolysis and condensation) of TetraEthyl OrthoSilicate (TEOS:Si(OCH₂CH₃)₄) as a precursor/starting material, 3) inorganic silicaobtained by dilution, ion-exchange, seed growth and concentrationreaction of sodium silicate (e.g., Water-glass/sodium silicate: Na₂SiO₃)as a precursor/starting material, and 4) inorganic silica obtained bygas-phase combustion reaction of tetrachlorosilane (SiCl₄) as aprecursor/starting material. Amongst the four silica preparationmethods, the most preferred method for charged abrasives used in thisdisclosure is the organic silica obtained from TMOS (Method 1 above).

The charged abrasives (i.e., the cationic or anionic abrasive) caninclude oxides, such as alumina, silica, titania, ceria, zirconia,co-formed products thereof, or mixtures thereof. In some embodiments,the cationic or anionic abrasive can include colloidal oxides, such ascolloidal alumina, colloidal silica, or colloidal titania.

In some embodiments, the cationic abrasive can include cationiccolloidal silica, or base immobilized non-ionic silica (e.g., non-ionicsilica physically or chemically modified to include basic groups). Insome embodiments, the cationic abrasive can include terminal groups offormula (I):—O_(m)—X—(CH₂)_(n)—Y  (I),in which m is an integer from 1 to 3; n is an integer from 1 to 10; X isCe, Al, Si, Ti, or Zr; and Y is a cationic amino or thiol group. In someembodiments, the cationic abrasive can include ceria having a meanparticle size of at least about 1 nm (e.g., at least about 10 nm, atleast about 100 nm, at least about 200 nm, at least about 300 nm, atleast about 400 nm, or at least about 500 nm) to at most about 1000 nm(e.g., at most about 900 nm, at most about 800 nm, or at most about 700nm).

In some embodiments, the anionic abrasive can include anionic colloidalsilica, or acid immobilized non-ionic silica (e.g., non-ionic silicaphysically or chemically modified to include acidic groups). In someembodiments, the anionic abrasive can include terminal groups of formula(I):—O_(m)—X—(CH₂)_(n)—Y  (I),in which m is an integer from 1 to 3; n is an integer from 1 to 10; X isCe, Al, Si, Ti, or Zr; and Y is an acid group.

The “anionic group” mentioned herein can be an acid such as sulfonicacid, phosphoric acid, or carboxylic acid, or an anionic salt of any ofthese acids. The “cationic group” is typically an amino group (—NH₂), athiol (—SH) group, or a metal salt (such as a Na, K, or Al salt) or acationic salt of any of these or related bases. For example, a silanecoupling agent such as (CH₃O)₃Si(CH₂)₃—NH₂ with a terminal —NH₂ groupcan be used to obtain cationic silica with a terminal —NH₂ base group,which is often referred to as base immobilized non-ionic silica.Commercially available charged abrasives are available from thefollowing vendors—charged ceria from Solvay of Belgium, charged aluminafrom Evonik Industries of Germany, and charged silica from Fuso ChemicalCo., Ltd. of Japan and Nalco Company of IL, USA. In the presentdisclosure, “charged abrasives” mean negatively- or positively-chargedabrasives and include for example, the aforementioned commerciallyavailable charged abrasives from their respective vendors. They alsoinclude in-house abrasives chemically modified by anionic/cationicgroups (such as acid immobilization), in-situ charge modified abrasives,abrasives physically modified by multiple monolayer formation orphysical surface adsorption, or abrasives modified by any other suitablemethods to impart the desired charge. These charged abrasives can beused in combination with one or more other chemicals to obtain polishingcomposition having various dielectric film removal rates.

In this invention, it is preferred that the charged abrasives and/or thepolishing compositions containing those abrasives have a zeta potentialin the range of about 0 mV to about ±100 mV (e.g., from about ±5 mV toabout ±90 mV and from about ±10 mV to about ±80 mV). For example, thecationic abrasives and polishing compositions containing those abrasivescan have zeta potential (e.g., a positive zeta potential) in the 0 to+100 mV range (e.g., from about 1 to about +100 mV, from about +5 mV toabout +90 mV, from about +10 mV to about +80 mV, from about +20 mV toabout +70 mV, or from about +30 mV to about +50 mV) in the 2-7 (e.g.,2-6) pH regime, whereas the anionic abrasives and polishing compositionscontaining those abrasives can have zeta potential (e.g., a negativezeta potential) in the 0 to −100 mV range (e.g., from about −1 to about−100 mV, from about −5 mV to about −90 mV, from about −10 mV to about−80 mV, from about −20 mV to about −70 mV, from about −30 mV to about−60 mV, or from about −40 mV to about −50 mV) in the 2-7 (e.g., 2-6) pHregime. This is illustrated in FIG. 2.

The charge of the polishing compositions described herein can also bemeasured by their electrical conductivity. For example, the polishingcompositions can have a conductivity in the range of from about 0.01 toabout 100 milli-Siemens per centimeter (mS/cm), or any subrangestherebetween, from about 0.1 to about 10 mS/cm, or any subrangestherebetween, or from about 0.5 to about 5 mS/cm, or any subrangestherebetween.

The charged abrasive (cationic or anionic) may be present in a polishingcomposition in an amount from about 0.01 wt % to about 50 wt %, based onthe total weight of the composition, or any subranges therebetween, orabout from 0.05 wt % to about 40 wt %, based on the total weight of thecomposition, or any subranges therebetween. For example, the cationic oranionic abrasive can be present in an amount of at least about 0.01 wt %(e.g., at least about 0.1 wt %, at least about 0.5 wt %, at least about1%, or at least about 5 wt %) to at most about 50 wt % (e.g., at mostabout 40 wt %, at most about 30 wt %, at most about 25 wt %, at mostabout 20 wt %, at most about 10 wt %, or at most about 5 wt %) based onthe total weight of the polishing composition.

The polishing compositions of the present disclosure, in addition tocharged abrasives, can contain a pH adjuster (e.g., an acid, a base, orboth) to adjust the pH to the operating pH of the polishing composition.Suitable acids to adjust pH include (but are not limited to) carboxylicacids such as formic acid, acetic acid, malonic acid, citric acid,propionic acid, malic acid, adipic acid, succinic acid, lactic acid,oxalic acid, hydroxyethylidene diphosphonic acid,2-phosphono-1,2,4-butane tricarboxylic acid, aminotrimethylenephosphonic acid, hexamethylenediamine tetra(methylenephosphonic acid),bis(hexamethylene) triamine phosphonic acid, amino acetic acid,peracetic acid, potassium acetate, phenoxyacetic acid, glycine, bicine,diglycolic acid, glyceric acid, tricine, alanine, histidine, valine,phenylalanine, proline, glutamine, aspartic acid, glutamic acid,arginine, lysine, tyrosine, or benzoic acid, and inorganic acids such asnitric acid, sulfuric acid, sulfurous acid, phosphoric acid, phosphonicacid, hydrochloric acid, periodic acid or any combinations thereof.Suitable bases to adjust pH include (but are not limited to) potassiumhydroxide, sodium hydroxide, cesium hydroxide, ammonium hydroxide,triethanol amine, diethanol amine, monoethanol amine, tetrabutylammonium hydroxide, tetramethyl ammonium hydroxide, lithium hydroxide,and any azole containing bases such as imidazole, triazole,aminotriazole, tetrazole, benzotriazole, tolytriazole, pyrazole orisothiazole, and any combinations thereof.

In some embodiments, the pH adjustor (e.g., an acid, a base, or both)can be present in an amount of from at least about 0.0001 wt % (e.g., atleast about 0.001 wt %, at least about 0.01 wt %, at least about 0.1 wt%, at least about 0.5 wt %, at least about 1 wt %, at least about 5 wt%, or at least about 10 wt %) to at most about 30 wt % (e.g., at mostabout 25 wt %, at most about 20 wt %, at most about 15 wt %, at mostabout 10 wt %, at most about 5 wt %, or at most about 1 wt %) based onthe total weight of a polishing composition described herein.

In some embodiments, the polishing compositions described herein caninclude a liquid medium, such as water. In some embodiments, the watercan be in an amount of from at least about 20 wt % (e.g., at least about30 wt %, at least about 40 wt %, at least about 50 wt %, at least about60 wt %, at least about 70 wt %, at least about 80 wt %, at least about90 wt %, or at least about 95 wt %) to at most about 99 wt % (e.g., atmost about 98 wt %, at most about 97 wt %, at most about 96 wt %, or atmost about 95 wt %) of a polishing composition described herein.

In some embodiments, the polishing compositions containing cationic oranionic abrasives described herein can be substantially free of one ormore of certain ingredients, such as halide salts, polymers (e.g.,cationic or anionic polymers), surfactants, plasticizers, oxidizingagents, corrosion inhibitors (e.g., azole or non-azole corrosioninhibitors), and/or non-ionic abrasives. The halide salts that can beexcluded from the polishing compositions include alkali metal halides(e.g., sodium halides or potassium halides) or ammonium halides (e.g.,ammonium chloride), and can be chlorides, bromides, or iodides. As usedherein, an ingredient that is “substantially free” from a polishingcomposition refers to an ingredient that is not intentionally added intothe polishing composition. In some embodiments, the polishingcompositions described herein can have at most about 1000 ppm (e.g., atmost about 500 ppm, at most about 250 ppm, at most about 100 ppm, atmost about 50 ppm, at most about 10 ppm, or at most about 1 ppm) of oneor more of the above ingredients that are substantially free from thepolishing compositions. In some embodiments, the polishing compositionsdescribed can be completely free of one or more the above ingredients.

The pH of the composition of the present disclosure can be from about 2to about 7, or any subranges therebetween. The pH can also be from about3 to about 6, or any subranges therebetween, or from about 3.4 to about5.75, or any subranges therebetween. For example, the pH can be from atleast about 2 (e.g., at least about 2.5, at least about 3, at leastabout 3.5, at least about 4, at least about 4.5, or at least about 5) toat most about 7 (e.g., at most about 6.5, at most about 6, at most about5.5, at most about 5, at most about 4.5, or at most about 4). The pH canbe measured using a pH meter, such as those available from the companyThermo Fisher Scientific.

In some embodiments, the charged (cationic or anionic) abrasivesdescribed herein can have a mean particle size of from about 1 nm to5000 nm (e.g., from about 1 nm to 1000 nm, from about 1 nm to 500 nm,and about 1 nm to 150 nm), or any subranges thereof. For example, thecharged abrasives can have a mean particle size of from at least about 1nm (e.g., at least about 5 nm, at least about 10 nm, at least about 50nm, at least about 100 nm, at least about 200 nm, at least about 300 nm,at least about 400 nm, or at least about 500 nm) to at most about 5000nm (e.g., at most about 2500 nm, at most about 1000 nm, at most about750 nm, at most about 500 nm, at most about 250 nm, or at most about 100nm). Without wishing to be bound by theory, it is believed that anionicabrasives having a smaller particle size have the advantage ofpreferentially giving lower (TEOS) RRs, and thus improving the overallselectivity to SiO₂ in systems where lower TEOS rates are needed(anionic silica systems). Conversely, it is believed that cationicabrasives having a larger particle size have the advantage ofpreferentially giving higher SiO₂ (TEOS) RRs, and thus improving theoverall selectivity to SiO₂ in systems where higher SiO₂ rates areneeded (cationic silica systems). Further, it is believed that, foranionic silica systems where high SiN film rates are needed, a smallerparticle size gives higher SiN removal rates because smaller particleshave a higher overall surface area and thus increase SiN film removalrates as the active binding sites on the silica increases with thesurface area increase. As used herein, “particle size” used in thisdisclosure is the mean particle size (MPS) determined by dynamic lightscattering techniques. For instance, the MPS can be measured by using acommercial dynamic light scattering tool from Malvern Instruments Ltd.

In the discussion above and in the following examples, the compositionsof the present disclosure are discussed in combination with polishingthe most prevalent dielectric films, i.e., SiN films, SiO₂ (TEOS) films,and P—Si films. However, present compositions can also be used to polishsilicon carbide (SiC), silicon carbide nitride (SiC_(x)N_(y)), siliconcarbide oxide (SiC_(x)O_(y)), spin-on-carbon (C), Carbon only (C), andsilicon carbide hydride (SiC_(x)H_(y)). Furthermore, the dielectricmaterials polished can be low-k dielectric (SiC_(x)O_(y)H_(z)), andultra-low k (ULK) dielectric (SiC_(x)O_(y)H_(z)) materials. Some commonexamples of low-k and ULK dielectric materials are Black Diamond I andII, respectively, from Applied Materials.

In some embodiments, the CMP polishing compositions or slurriesdescribed herein can be used to polish patterned wafers that contain aheterogeneous combination of metal and dielectric films at variousdensities and thickness levels. An end goal of CMP compositions is toflatten and planarize all the peaks and valleys on a patterned wafer.Thus, the polishing compositions of the present disclosure, when used topolish dielectric films, can also polish metal, metal oxide, or metalnitride films on patterned wafers. Common examples of metals that can bepolished include copper, ruthenium, cobalt, aluminum, tantalum,titanium, and tungsten. Similarly, common examples of metal oxides thatcan be polished include hafnium oxide, titanium oxide, zirconium oxide,tantalum oxide, aluminum oxide, tungsten oxide, and yttrium oxide.Common examples of metal nitrides that can be polished include tantalumnitride, titanium nitride, tungsten nitride and cobalt nitride. Thus,the polishing compositions of the present disclosure can at any timeduring polishing of patterned wafers polish a multitude of dielectricand metal/metal oxide/metal nitride films as per the integrationrequirements.

In general, this disclosure also features methods of using one or moreof the polishing compositions described herein.

In some embodiments, this disclosure features a polishing method using apolishing composition containing a cationic abrasive. In suchembodiments, the method can include (a) applying a polishing compositionto a substrate having silicon nitride and at least one of silicon oxideand polysilicon on a surface of the substrate, in which the compositionincludes a cationic abrasive, an acid or base, and water, and thecomposition has a pH of about 2 to about 7; and (b) brining a pad intocontact with the substrate and moving the pad in relation to thesubstrate. The substrate can be a semiconductor substrate, such as apatterned wafer. In such embodiments, the method can remove at least aportion of at least one of silicon oxide and polysilicon at a firstrate, the method can remove at least a portion of silicon nitride at asecond rate, and a ratio of the first rate to the second rate is atleast about 2:1. In some embodiments, the ratio of the first rate to thesecond rate can be at least about 3:1 (e.g., at least about 4:1, atleast about 5:1, at least about 6:1, at least about 7:1, at least about8:1, at least about 9:1, at least about 10:1; at least about 15:1, atleast about 20:1, or at least about 50:1) or at most about 200:1 (or atmost about 100:1).

In some embodiments, the zeta potential difference between the polishingcomposition containing a cationic abrasive and silicon oxide orpolysilicon is at least about 20 mV (e.g., at least about 30 mV, atleast about 40 mV, at least about 50 mV, at least about 60 mV, at leastabout 70 mV, at least about 80 mV, at least about 90 mV, or at leastabout 100 mV) and at most about 200 mV (e.g., at most about 150 mV). Insome embodiments, the zeta potential difference between the polishingcomposition containing a cationic abrasive and silicon nitride is atmost about 20 mV (e.g., at most about 15 mV, at most about 10 mV, atmost about 5 mV, or at most about 1 mV) or about 0 mV. Without wishingto be bound by theory, it is believed that, when a polishing compositioncontaining a cationic abrasive has a relatively large zeta potentialdifference relative to silicon oxide or polysilicon and a relativelysmall zeta potential difference relative to silicon nitride, thepolishing composition can selectively remove silicon oxide orpolysilicon without removing silicon nitride in any substantial amount(i.e., stop on SiN).

In some embodiments, the polishing method that uses a polishingcomposition containing a cationic abrasive can remove substantially allof silicon oxide and/or substantially all of polysilicon on thesubstrate. In some embodiments, such a polishing method can furtherinclude a step of removing at least some (e.g., substantially all) ofsilicon nitride on the substrate (e.g., by using a polishing compositioncontaining an anionic abrasive).

In some embodiments, this disclosure features a polishing method using apolishing composition containing an anionic abrasive. In suchembodiments, the method can include (a) applying a polishing compositionto a substrate having silicon nitride and polysilicon on a surface ofthe substrate, in which the composition includes an anionic abrasive, anacid or base, and water, and the composition has a pH of about 2 toabout 7; and (b) brining a pad into contact with the substrate andmoving the pad in relation to the substrate. The substrate can be asemiconductor substrate, such as a patterned wafer. In such embodiments,the method can remove at least a portion of silicon nitride at a firstrate, the method removes at least a portion of polysilicon at a secondrate, and a ratio of the first rate to the second rate is at least about2:1. In some embodiments, the ratio of the first rate to the second ratecan be at least about 3:1 (e.g., at least about 4:1, at least about 5:1,at least about 6:1, at least about 7:1, at least about 8:1, at leastabout 9:1, at least about 10:1; at least about 15:1, at least about20:1, or at least about 50:1) or at most about 200:1 (or at most about100:1).

In some embodiments, the zeta potential difference between the polishingcomposition containing an anionic abrasive and silicon nitride is atleast about 20 mV (e.g., at least about 30 mV, at least about 40 mV, atleast about 50 mV, at least about 60 mV, at least about 70 mV, at leastabout 80 mV, at least about 90 mV, or at least about 100 mV) and at mostabout 200 mV (e.g., at most about 150 mV). In some embodiments, the zetapotential difference between the polishing composition containing ananionic abrasive and polysilicon in at most about 20 mV (e.g., at mostabout 15 mV, at most about 10 mV, at most about 5 mV, or at most about 1mV) or about 0 mV. Without wishing to be bound by theory, it is believedthat, when a polishing composition containing an anionic abrasive has arelatively large zeta potential difference relative to silicon nitrideand a relatively small zeta potential difference relative topolysilicon, the polishing composition can selectively remove siliconnitride without removing polysilicon in any substantial amount (i.e.,stop on polysilicon).

In some embodiments, the polishing method that uses a polishingcomposition containing an anionic abrasive can remove substantially allof silicon nitride on the substrate. In some embodiments, such apolishing method can further include a step of removing at least some(e.g., substantially all) of polysilicon on the substrate (e.g., byusing a polishing composition containing a cationic abrasive).

In some embodiments, the polishing method that uses a polishingcomposition containing a cationic abrasive or an anionic abrasive canfurther include producing a semiconductor device from the substratetreated by a polishing composition described herein through one or moreadditional steps.

The contents of all publications cited herein (e.g., patents, patentapplication publications, and articles) are hereby incorporated byreference in their entirety.

EXAMPLES

Examples are provided to further illustrate the capabilities of thepolishing compositions and methods of the present disclosure. Theprovided examples are not intended and should not be construed to limitthe scope of the present disclosure.

Overview of Examples and Figures

FIGS. 1 and 2 illustrate the overall concept of using charged abrasivefor selective polishing of dielectrics. FIG. 3 (Example 1: Anionicsilica for High SiN/SiO₂ selectivity), FIG. 4 (Example 2: Anionic silicafor High SiN/P—Si selectivity), and FIG. 5 (Example 3: Cationic silicafor High SiO₂/SiN selectivity) show that actual experimental results areconsistent with the above concept.

FIG. 1 shows that, in Case I, when anionic silica is used, the surfacecharge of the silica and consequently the slurry is negative. FIG. 1also shows the surface charge of the three tested dielectric films(i.e., SiN, SiO₂, and P—Si films). As can be seen in Case I, SiN filmsinclude positive charges and SiO₂ films include negative charges. TheP—Si films include much more negative charges than the SiO₂ films. Inother words, SiN, SiO₂, and P—Si films follow the following negativecharge scale, P—Si>>SiO₂>>SiN. This electrostatic charge of the films isalso depicted further in FIG. 2 as zeta potential versus pH values.Thus, for Case I, based on electrostatic forces of attraction and/orrepulsion (attraction means silica and a film attract and thus give highremoval rates (RRs); conversely, repulsion means that silica and a filmrepel and thus give low RRs for that film), it is hypothesized thatanionic silica (A) will give high SiN RRs and give low RRs on SiO₂ andP—Si films. Experimental confirmation of this hypothesis is seen inFIGS. 3 and 4.

Conversely, for Case II, an example of cationic silica (C) is shown,wherein the silica, and consequently the CMP slurry containing suchsilica, has positive surface charge/zeta potential. FIG. 2 gives thezeta potential/surface charge of the cationic silica and the SiN, SiO₂and P—Si films in the pH range of 2-11. In Case II shown in FIG. 1, itis hypothesized that cationic silica (C) will give high RRs on SiO₂and/or P—Si films, and will give low RRs on SiN films. Experimentalconfirmation of this hypothesis is seen in FIG. 5.

Example 1: Anionic Silica for High SiN/SiO2 Selectivity

This example demonstrates the use of anionic silica (negatively chargedsilica) in CMP slurry compositions that resulted in high SiN removalrates (RRs) and low SiO₂ removal rates.

In this example, the polishing compositions or slurries included 1 wt %anionic silica abrasive, an acid and a base as pH adjustors, and wateras a liquid carrier. The anionic silica abrasive was purchased from FusoChemical Co., Ltd. of Japan. The CMP slurries containing the anionicabrasive were pH adjusted with the pH adjustors to obtain slurries at pHinterims of 0.5 pH value in the ^(˜)2-6.5 acidic pH range. For alltested formulations, an Applied Materials Mirra CMP polisher was usedwith a downforce of 2 psi and a flow rate of 175 mL/min to polish 8 inchsilicon nitride and silicon oxide blanket wafers. The polishing resultsexpressed as removal rates for SiN and SiO₂ films are summarized inTable 1.

TABLE 1 Anionic abrasive containing slurry's RRs and selectivities onSiN and SiO₂ films. Graphical representation of the data is in FIG. 3.SiN/SiO₂ selectivity Slurry~pH SiN RR (A/min) SiO₂ RR (A/min) ratio 2817 109 7 2.5 725 32 23 3 654 16 41 3.5 591 15 39 4 491 11 45 5 209 5 426 49 12 4

The zeta potentials (ZPs) of anionic silica were measured by usingAcoustoSizer II made by Colloidal Dynamics, and the ZPs of SiN films andTEOS films were measured by SurPASS 3 made by Anton Paar. The resultsare summarized in Table 2. Table 2 also details the charge separation(absolute value of ZP difference) between the SiN films and anionicsilica and between the SiO₂ films and anionic silica.

TABLE 2 Zeta potential and Charge separation values (mV) of anionicsilica and SiN and TEOS films. Graphical representation of the data isin FIG. 2. Charge separation/ Absolute value (mV) Zeta Potential of Zetadifference Values (mV) of between film & silica various films and SiNfilms SiO₂ films charged silica (+ve) & (−ve) & Approximate SiN SiO₂Anionic anionic silica anionic silica pH films films silica (−ve) (−ve)2 38  −6 −48 86 42 3 48 −12 −54 102  42 4 45 −28 −46 91 18 5 15 −32 −4964 17 6  7 −55 −50 57  5

As shown in Table 2, when the pH values of the CMP compositions are from2 to 6, the SiN films are positively charged (i.e., its ZPs arepositive), whereas the anionic silica is negatively charged (i.e., itsZPs are negative). As a result, there are attraction forces between SiNand anionic silica, which is believed to result in high RRs for SiNfilms, as can be seen in Table 1 and FIG. 3. Conversely, both the SiO₂films and the anionic silica are negatively charged (i.e., their ZPs arenegative). As a result, there are repulsion forces between SiO₂ andanionic silica, which is believed to result in low RRs for SiO₂ films,as can be seen in Table 1 and FIG. 3. Indeed, as shown in Table 1, theCMP compositions containing anionic silica abrasive exhibited high SiNremoval rates, low SiO₂ removal rates, and relatively high SiN/SiO₂removal selectivity (i.e., preferentially removing SiN over SiO₂).

In particular, Table 2 shows that, when pH ranges from 2 to 4, thecharge separation is the greatest between SiN films and anionic silica.In this pH range, the SiN RRs are the highest (between 817 A/min and 491A/min; see Table 1) indicating that, due to greater charge separation,there are stronger forces of attraction between positively charged SiNfilms and negatively charged anionic silica, thereby leading to higherRRs for SiN films. Conversely, Table 2 shows that, when pH ranges from 4to 6, the charge separation is the least between SiO₂ films and anionicsilica (both of which are negatively charged). In this pH range, SiO₂films and anionic silica repel each other the most and thus provide thelowest SiO₂ films RRs (between 5 A/min and 12 A/min; see Table 1).

The CMP slurry compositions discussed in Example 1 could be used inintegrations where, on patterned wafers, a high selectivity ratiobetween SiN and SiO₂ films is desired. In the industry, these aretypically referred to as Reverse-STI (Shallow Trench Isolation)selectivity schemes where it is desirable to remove SiN films at highRRs and minimize removal of SiO₂ films at very low to zero RRs.

Example 2: Anionic Silica for High SiN/P—Si Selectivity

This example demonstrates the use of anionic silica (negatively chargedsilica) in CMP slurry compositions that resulted in high SiN removalrRates and low P—Si (poly-silicon) removal rates.

In this example, the polishing composition included 1 wt % anionicsilica abrasive, an acid and a base as pH adjustors, and water as aliquid carrier. The anionic silica abrasive was purchased from FusoChemical Co., Ltd. of Japan. The CMP slurries containing the anionicabrasive were pH adjusted with the pH adjustors to obtain slurries at pHinterims of ^(˜)0.5 pH value in the ^(˜)2-6.5 acidic pH range. For alltested formulations, an Applied Materials Mirra CMP polisher was usedwith a downforce of 2 psi and a flow rate of 175 mL/min to polish 8 inchsilicon nitride and P—Si blanket wafers. The polishing results expressedas removal rates for SiN and P—Si films are summarized in Table 3.

TABLE 3 Anionic abrasive containing slurry's RRs and selectivities onSiN and P—Si films. Graphical representation of the data is in FIG. 4.SiN/P—Si SiN RR P—Si RR selectivity Slurry~pH (A/min) (A/min) ratio 2817 101 8 2.5 725 95 7 3 654 78 8 3.5 591 100 6 4 491 111 4 5 209 135 26 49 22 2

The zeta potentials (ZPs) of anionic silica were measured by usingAcoustoSizer II made by Colloidal Dynamics, and the ZPs of SiN films andP—Si films were measured by SurPASS 3 made by Anton Paar. The resultsare summarized in Table 4. Table 4 also details the charge separation(absolute value of ZP difference) between the SiN films and anionicsilica and between the P—Si films and anionic silica.

TABLE 4 Zeta potential and charge separation values (mV) of anionicsilica and SiN and P—Si films. Graphical representation of the data isin FIG. 2. Charge separation/ Absolute value (mV) of Zeta differencebetween film & silica Zeta Potential Values SiN films P—Si films (mV) ofvarious films (+ve) & (−ve) & and “charged” silica anionic anionicApproximate SiN P—Si Anionic silica silica pH films films silica (−ve)(−ve) 2 38 −26 −48 86 22  3 48 −38 −54 102  16  4 45 −39 −46 91 7 5 15−53 −49 64 4 6  7 −57 −50 57 7

As shown in Table 3, when the pH values of the CMP compositions rangefrom 2 to 7, the SiN films are positively charged, whereas the anionicsilica is negatively charged. As a result, there are attraction forcesbetween SiN films and anionic silica, which is believed to result inhigh RRs for SiN films, as can be seen in Table 3 and FIG. 4.Conversely, both the P—Si films and the anionic silica are negativelycharged (i.e., their ZPs are negative). As a result, there are repulsionforces between the P—Si films and the anionic silica, which is believedto result in low RRs for P—Si films, as can be seen in Table 3 and FIG.4. Indeed, as shown in Table 3, the CMP compositions containing anionicsilica abrasive exhibited high SiN removal rates, low P—Si removalrates, and relatively high SiN/P—Si removal selectivity (i.e.,preferentially removing SiN over P—Si).

The SiN/P—Si selectivity (i.e., from 2-8) is somewhat less than theSiN/SiO₂ selectivity (i.e., from 4 to 45). This lower SiN/P—Siselectivity can be attributed to the slightly higher P—Si RRs (whencompared to SiO₂ RRs) in the 3-5 pH range. It is believed that thesurface chemistry of TEOS films is slightly different from the surfacechemistry of P—Si films. The SiO₂ films include terminal silanol groups(Si—OH) on their surfaces, whereas the P—Si films include terminalhydride groups (Si—H) on their surfaces. Thus, it is believed that therepulsion forces are more pronounced between SiO₂ films and the anionicsilica in the polishing compositions because the anionic silica also hassilanol (Si—OH) surface groups. Therefore, it is believed that thenegative charge on the silanol group in the anionic silica repels thenegative charge on the surface silanol groups (Si—OH) of the SiO₂ films,thereby generating relatively strong forces of repulsion andconsequently reducing the SiO₂ RRs. Conversely, the hydrogen from thehydride groups (Si—H) on the P—Si films is not negatively charged andthus does not repel the anionic silica as strongly as the SiO₂ films,thereby giving higher P—Si film RRs when compared to the TEOS films. Asa result, it is believed that the SiN/P—Si selectivity is lower than theSiN/SiO₂ selectivity when using anionic silica containing CMPcompositions to polish these films, which has been confirmed by theexperiments described above.

On the other hand, the general concept of charged abrasive containingCMP composition design for specific dielectric film rate selectivitiesis still applicable. As shown above, SiN films having a positive ZPdisplay very high RRs due to attraction forces with anionic silica andP—Si films having a negative ZP exhibit low RRs due to repulsion forceswith anionic silica. Thus, an anionic abrasive containing CMPcomposition could be used for semiconductor integration schemes wherehigh SiN and low P—Si removal rates are required. Many integrations inFEOL chip assembly require such selectivities on patterned wafers thathave additional conductors and/or insulators such as metals, metaloxides, metal nitrides, and dielectric films. The selectivity ofSiN/P—Si of 2-8 with the anionic abrasive containing CMP composition,although not as high as the SiN/SiO₂ selectivity, is still veryattractive for use in polishing patterned wafers containing SiN and P—Sifilms, where the goal is to remove the SiN films and stop on the P—Sifilms.

Example 3: Cationic Silica Abrasive for High SiO₂/SiN Selectivity

This example demonstrates the use of cationic silica (positively chargedsilica) in CMP slurry compositions that resulted in high SiO₂ removalrates and low SiN removal rates.

In this example, the polishing composition included 1 wt % cationicsilica abrasive, an acid and a base as pH adjustors, and water as aliquid carrier. The cationic silica abrasive was purchased from FusoChemical Co., Ltd. of Japan. The CMP slurries containing the cationicabrasive were pH adjusted with the pH adjustors to obtain slurries at pHinterims of ^(˜)0.5 pH value in the ^(˜)2-7 pH range. For all testedformulations, an Applied Materials Mirra CMP polisher was used with adownforce of 2 psi and a flow rate of 175 mL/min to polish 8 inchsilicon nitride and silicon oxide blanket wafers. The polishing resultsexpressed as removal rates for SiO₂ and SiN films are summarized inTable 5.

TABLE 5 Cationic abrasive containing slurry's RRs and selectivities onSiO₂ and SiN films. Graphical representation of the data is in FIG. 5.SiO₂/SiN SiO₂ RR SiN RR selectivity Slurry~pH (A/min) (A/min) ratio 2361 120 3 2.5 274 97 3 3 281 85 3 4 962 98 10  5 1015 261 4 6 392 244 27 95 86 1

The zeta potentials (ZPs) of cationic silica were measured by usingAcoustoSizer II made by Colloidal Dynamics, and the ZPs of SiN films andSiO₂ films were measured by SurPASS 3 made by Anton Paar. The resultsare summarized in Table 6. Table 6 also details the charge separation(absolute value of ZP difference) between the SiO₂ films and cationicsilica and between the SiN films and cationic silica.

TABLE 6 Zeta potential and charge separation values (mV) of cationicsilica and TEOS and SiN films. Graphical representation of the data isin FIG. 2. Charge separation/ Absolute value (mV) of Zeta differencebetween film & silica Zeta Potential Values SiO₂ films SiN films (mV) ofvarious films (−ve) & (+ve) & and “charged” silica cationic cationicApproximate SiN SiO₂ Cationic silica silica pH films films Silica (+ve)(+ve) 2 38  −6 38 44 0 3 48 −12 47 59 1 4 45 −28 42 70 3 5 15 −32 25 5710  6 7 −55  1 56 6

As shown in Table 6, when the pH values of the CMP compositions rangefrom 2 to 7, the SiO₂ films are negatively charged and the cationicsilica is positively charged. As a result, there are attraction forcesbetween SiO₂ films and cationic silica, which is believed to result inhigh RRs for SiO₂ films, as can be seen in Table 5 and FIG. 5.Conversely, both the SiN films and the cationic silica are positivelycharged (i.e., their ZPs are positive). As a result, there are repulsionforces between the SiN films and the cationic silica, which is believedto result in low RRs for SiN films, as can be seen in Table 5 and FIG.5. Indeed, as shown in Table 5, the CMP compositions containing cationicsilica abrasive exhibited high SiO₂ removal rates, low SiN removalrates, and relatively high SiO₂/SiN removal selectivity (i.e.,preferentially removing SiO₂ over SiN).

In particular, Table 6 shows that, when the pH of the CMP compositionsis from 4 to 5, the charge separation is the greatest between SiO₂ filmsand cationic silica. As a result, during this pH range, the SiO₂ RRs arethe highest (between 962 A/min and 1015 A/min; see Table 5), indicatingthat due to greater charge separation, there are stronger forces ofattraction between the negatively charged SiO₂ films and positivelycharged cationic silica, thereby leading to higher RRs for SiO₂ films.Conversely, Table 6 shows that, when the pH is 2, 3, and 4, the chargeseparation is the least between SiN films and cationic silica (both arepositively charged). In this pH range, SiN films and cationic silicarepel each other the most and thus provide the lowest SiN films RRs(i.e., 97 A/min, 85 A/min and 98 A/min respectively; see Table 5).Additionally, at relatively greater charge separation between SiN filmsand cationic silica at pH of 5 and 6 (charge separation of 10 and 6 mV,respectively; see Table 6), SiN films and cationic silica repel less andthe SiN RRs are relatively high (i.e., 261 A/min and 244 A/min,respectively). This is consistent with the design of using chargedabrasive-containing CMP compositions to achieve desired RRs andselectivities.

The CMP slurry compositions discussed in Example 3 containing cationicabrasives could be used in integrations where, on patterned wafers, ahigh selectivity ratio between SiO₂ and SiN films is desired. In theindustry, these are typically referred to as Shallow Trench Isolation(STI) processes wherein, the silicon oxide film (an insulator) separatesthe conducting metal wires (such as copper, tungsten, or othermetals/metal oxides), and the objective of the CMP process is to removethe SiO₂ films and stop-on SiN films on patterned wafers. There are manyother FEOL and/or BEOL integration schemes where a high selectivity CMPcomposition of SiO₂ films over SiN films is required during the CMPprocess, and the cationic abrasive containing CMP compositions could beused in such schemes to polish heterogeneous materials on patternedwafers.

While the present disclosure has been described with reference to one ormore exemplary embodiments, it will be understood by those skilled inthe art that various changes may be made and equivalents may besubstituted for elements thereof without departing from the scope of thepresent disclosure. Variations of the preferred embodiments mentionedherein may become apparent to those of ordinary skill in the art uponreading the foregoing descriptions. In addition, many modifications maybe made to adapt a particular situation or material to the teachings ofthe disclosure without departing from the scope thereof. Therefore, itis intended that the present disclosure not be limited to the particularembodiment(s) disclosed as the best mode contemplated, but that thedisclosure will include all embodiments falling within the scope of theappended claims. Furthermore, the inventors expect skilled artisans toemploy variations as appropriate to practice the disclosure in otherforms than as specifically described herein. This includes allmodifications and equivalents of the subject matter recited in theclaims appended hereto as permitted by applicable law.

What is claimed is:
 1. A polishing composition, comprising a) a cationic abrasive comprising alumina, silica, titania, zirconia, a co-formed product thereof, or a mixture thereof, wherein the cationic abrasive comprises terminal groups of formula (I): —O_(m)—X—(CH₂)_(n)—Y  (I), in which m is an integer from 1 to 3; n is an integer from 1 to 10; X is Al, Si, Ti, or Zr; and Y is a cationic amino group or a cationic thiol group; b) an acid or base; and c) water; wherein the polishing composition has a pH of about 2 to about 7, is free of a cationic polymer, and is substantially free of a halide salt; and wherein the polishing composition has a first rate of removal of silicon oxide, a second rate of removal of silicon nitride, and a ratio of the first rate to the second rate is at least about 2:1.
 2. The composition of claim 1, wherein the composition has a first rate of removal of polysilicon, a second rate of removal of silicon nitride, and a ratio of the first rate to the second rate is at least about 2:1.
 3. The composition of claim 1, wherein the cationic abrasive comprises colloidal alumina, colloidal silica, or colloidal titania.
 4. The composition of claim 1, wherein the cationic abrasive comprises cationic colloidal silica, or base immobilized non-ionic silica.
 5. The composition of claim 4, wherein the silica is prepared by a sol-gel reaction from tetramethyl orthosilicate.
 6. The composition of claim 1, wherein the cationic abrasive is present in the composition in an amount of from about 0.01 wt % to about 50 wt % based on the total weight of the composition.
 7. The composition of claim 1, wherein the acid is selected from the group consisting of formic acid, acetic acid, malonic acid, citric acid, propionic acid, malic acid, adipic acid, succinic acid, lactic acid, oxalic acid, hydroxyethylidene diphosphonic acid, 2-phosphono-1,2,4-butane tricarboxylic acid, aminotrimethylene phosphonic acid, hexamethylenediamine tetra(methylenephosphonic acid), bis(hexamethylene)triamine phosphonic acid, amino acetic acid, peracetic acid, potassium acetate, phenoxyacetic acid, glycine, bicine, diglycolic acid, glyceric acid, tricine, alanine, histidine, valine, phenylalanine, proline, glutamine, aspartic acid, glutamic acid, arginine, lysine, tyrosine, benzoic acid, nitric acid, sulfuric acid, sulfurous acid, phosphoric acid, phosphonic acid, hydrochloric acid, periodic acid, and mixtures thereof.
 8. The composition of claim 1, wherein the base is selected from the group consisting of potassium hydroxide, sodium hydroxide, cesium hydroxide, ammonium hydroxide, triethanolamine, diethanolamine, monoethanolamine, tetrabutylammonium hydroxide, tetramethylammonium hydroxide, lithium hydroxide, imidazole, triazole, aminotriazole, tetrazole, benzotriazole, tolytriazole, pyrazole, isothiazole, and mixtures thereof.
 9. The composition of claim 1, wherein the acid or base is present in the composition in an amount of from about 0.0001 wt % to about 30 wt % based on the total weight of the composition.
 10. The composition of claim 1, wherein the cationic abrasive has a mean particle size of from about 1 nm to about 5000 nm.
 11. The composition of claim 1, wherein the composition has a zeta potential of from about 0 mV to about +100 mV.
 12. The composition of claim 1, wherein the composition has a conductivity of from about 0.01 mS/cm to about 100 mS/cm.
 13. A method, comprising: applying the polishing composition of claim 1 to a substrate having silicon nitride and at least one of silicon oxide and polysilicon on a surface of the substrate; and brining a pad into contact with the substrate and moving the pad in relation to the substrate; wherein the method removes at least a portion of at least one of silicon oxide and polysilicon at a first rate, the method removes at least a portion of silicon nitride at a second rate, and a ratio of the first rate to the second rate is at least about 2:1.
 14. The method of claim 13, wherein the ratio of the first rate to the second rate is at least about 10:1.
 15. The method of claim 13, wherein the zeta potential difference between the polishing composition and silicon oxide or polysilicon is at least about 20 mV and the zeta potential difference between the polishing composition and silicon nitride is at most about 20 mV.
 16. The method of claim 13, wherein the method removes substantially all of the at least one of silicon oxide and polysilicon on the substrate.
 17. The method of claim 16, further comprises removing at least some of silicon nitride on the substrate.
 18. The method of claim 13, wherein the substrate further comprises an additional material selected from the group consisting of metals, metal oxides, metal nitrides and dielectric materials.
 19. The method of claim 13, further comprising producing a semiconductor device from the substrate treated by the polishing composition. 